1. Field of the Invention
This invention relates to radication curable coating compositions containing copolymerizable ultra-violet light absorber compounds, which can provide polymer materials with improved degradation to light.
2. Description of the Prior Art
Coating compositions which are curable under the influence of radiation in general and ultra-violet light as well as electron beam in particular are well known. Representative examples of prior coating compositions include those disclosed in U.S. Pat. Nos. 3,782,961; 3,829,531; 3,850,770; 3,874,906; 3,864,133; 3,891,523; 3,895,171; 3,899,611; 3,907,574; 3,912,516; 3,932,356; and 3,989,609. Unfortunately, these coating compositions suffer from a number of disadvantages and do not have an in situ ultra-violet absorber in the composition. Many of these coating compositions have insufficient flexibility that causes them to crack when applied to flexible substrates such as those of polyvinyl chloride. Other compositions do not adhere sufficiently to the substrate with the undesirable result that they become dislodged or peel. Still other coating compositions require the use of solvents that must be evaporated during the curing process. The evaporation of such solvents consumes energy and creates atmospheric pollution problems. Other compositions produce coatings that yellow, do not weather well, and have insufficient scratch-resistance, stain-resistance, abrasion-resistance, and/or solvent-resistance.
The use of ultra-violet absorbers in plastics or coatings to enhance weather resistance is known. The absorbers absorb the radiation and dissipate the energy and thus protect the coating from structural degradation. Considerable economic saving is realized by incorporating the ultra-violet absorber on the surface of a plastic article rather than using the ultra-violet absorber in conventional bulk application. Conventional surface application, such as the use of a solvent or paint vehicle is, moreover, undesirable in view of the pollution hazard and bulk handling procedures. Radiation curing has made possible production of coating films which are easier to handle, but heretofore ultra-violet absorbers have consumed the energy from the radiation source resulting in too high energy demands in curing or too slow curing rates. If a small amount of ultra-violet photoinitiator is used to facilitate curing, then addition of use levels of most ultra-violet stabilizers would prevent the curing from occurring.
Accordingly, it is an object of the present invention to provide an improved coating composition that is substantially free of one or more of the disadvantages of prior radiation curable coating compositions.
Yet another object is to provide a coating composition that will produce a coating that is weather-resistant, non-yellowing, scratch-resistant, stain-resistant, abrasion-resistant, and solvent-resistant.
Yet another object is to provide a coating composition that is free of volatile solvents.
Another object is to provide an improved process for coating substrates such as those of natural leather, synthetic leather, polyvinyl chloride, polyurethanes and polycarbonates.
Still another object is to provide a coating composition with a copolymerizable ultra-violet absorber which can be cured by radiation.
Other objects and advantages of the present invention will be apparent to those skilled in the art by reference to the following detailed description.